1. Field of the Invention
This invention relates to electrolytes for Karl Fischer coulometric titrations, and more specifically, it relates to electrolytes for Karl Fischer coulometric titrations free from disagreeable odors ahd having improved functions.
2. Description of the Prior Art
Karl Fischer coulometric titration methods are known, and as electrolytes, those chiefly comprising iodine, sulfur dioxide, pyridine and methanol are generally employed. On actual measurement, iodine is present as iodide ions, and when a sample is introduced, iodine is simultaneously generated by electrolysis, thereby the Karl Fischer reaction proceeds. Therefore, electrolytes utilizing potassium iodide or sodium iodide instead of the iodine are also used.
Since conventional electrolytes for Karl Fischer coulometric titrations have contained pyridine having specific odors as one of their components, analytical operations have been inconvenient. Therefore, electrolytes free from pyridine odors have been desired. Further, in general, electrolytes for Karl Fischer coulometric titrations use methanol as a main solvent in order to easily dissolve a sample and so that the Karl Fischer reaction proceeds more quantitatively. However, where a ketone, such as acetone etc., or a carboxylic acid, such as acetic acid etc., is present in a sample, the aforesaid methanol and the ketone or the carboxylic acid react as shown in the following formulae: ##STR3## wherein R, R' and R" each represent an alkyl group, to generate water, and thus interferring with the water measurement. In order to avoid such interfering reactions, there may be contemplated a method of conducting water measurement at low temperatures, but even at low temperatures, it is impossible to completely inhibit said reactions and thus the obtained results would lack accuracy. Therefore, the electrolytes for Karl Fischer coulometric titrations using methanol as a main solvent were not suitable for water measurement in ketones, carboxylic acids or samples containing them, and the advent of an electrolyte which may easily be applied to samples containing ketones etc. has been sought. Recently, as electrolytes free from pyridine odors, electrolytes using various aliphatic amines, heterocyclic compounds etc., instead of the pyridine have been proposed (Japanese Patent Application Laid-open No. 137250/1981).
On the other hand, as an electrolyte, an electrolyte in which the reaction rate for the Karl Fischer reaction is higher is desirable from the aspect that the titration time may be shortened, and an electrolyte in which the change in electric potential near the titration end point is mild is desirable from the aspect that the control of the equipment is easy and also the measurement accuracy may be improved. However, the above-described known electrolytes have not been always satisfactory from this viewpoint.
Furthermore, as electrolytes for samples containing ketones, electrolytes using chloroform and an alkylene carbonate as a main solvent have been proposed (Japanese Patent Application Laid-open No. 112641/1981). However, further improvement has been sought from the viewpoint that they have pyridine odors.
The present inventors have further continued their study for the purpose of presenting electrolytes for Karl Fischer coulometric titration which satisfy the above-described requirements, and have discovered that by using specific amines and further by selecting a specific solvent, the aimed object may be achieved, thereby having accomplished this invention.